The present invention relates to an electro-optical device which comprises a conductive layer having a light-shielding function, and a method of manufacturing the electro-optical device.
A liquid crystal device is constructed by sealing liquid crystal between two substrates which are made of glass substrates, quartz substrates, or the like. In the liquid crystal device, active elements, such as thin film transistors (hereinafter, referred to as ‘TFTs’), and pixel electrodes are arranged in a matrix shape on the one of two substrates. On the other substrate, a counter electrode (transparent electrode (ITO (indium tin oxide)) is arranged. In this way, the optical properties of the liquid crystal layer sealed between both substrates change according to image signals, such that image display can be implemented.
In an electro-optical device, such as an active matrix driving type liquid crystal device using the active elements, the pixel electrodes and switching elements are provided on the substrate (active matrix substrate) corresponding to intersections of a plurality of scanning lines (gate lines) and a plurality of data lines (source lines) which are arranged in longitudinal and traverse directions, respectively.
The switching element, such as the TFT element, is turned on by an ON signal which is supplied to the gate line, and the image signal which is supplied through the source line is written into the pixel electrode (transparent electrode (ITO)). Thus, voltage based on the image signal is applied to the liquid crystal layer between the pixel electrode and the counter electrode, and the alignment states of liquid crystal molecules change. In this way, transmittance of a pixel changes and light passing through the pixel electrode and the liquid crystal layer changes according to the image signal, such that the image display can be implemented.
In the case where elements constituting an element substrate are formed in one plane on the substrate, the occupied area of each element increases and the area of the pixel electrode is reduced, such that the pixel opening ratio is lowered. Therefore, conventionally, a laminated structure in which the elements are separately formed in the respective one of plural layers and interlayer insulating films are disposed between the respective layers is adopted.
Specifically, the element substrate is constructed by laminating a semiconductor thin film, an insulating thin film, or a conductive thin film with a predetermined pattern on a glass or quartz substrate. A TFT substrate or the like is formed by repeatedly performing a film formation step and a photolithography step over various films.
For example, on the TFT substrate, the semiconductor layer constituting a channel of the TFT element, a wiring layer for the data line or the like, or a pixel electrode layer made of an ITO film are laminated. The pixel electrode layer is formed near the liquid crystal layer as an uppermost layer of the active matrix substrate and the pixel electrode is connected to the semiconductor layer through the wiring layer. Generally, the wiring layer for the data line or the like is made of aluminum. However, if aluminum and the ITO film are connected with each other through a contact hole, an electrolytic corrosion that the ITO film blacks due to an alkali delamination solution used for patterning is caused.
Therefore, in order to prevent the electrolytic corrosion, a multilayered wiring layer in which titanium nitride (TiN) is laminated on aluminum is adopted.
Further, for example, when aluminum as the conductive layer is connected with aluminum through a contact hole, a contact resistance increases due to the oxidization of aluminum. In this case, in order to reduce the contact resistance between aluminum and aluminum, an aluminum wiring line also has a multilayered structure of aluminum and titanium nitride.
In an electro-optical device, in order to prevent the TFT element from erroneously operating due to light incident thereon, a light-shielding film is formed. Further, the electro-optical device having the multilayered structure, it is constructed such that the conductive layer such as aluminum also serves as the light-shielding layer. Thus, reflected light or irregularly reflected light, as well as incident light, is effectively prevented from entering into the TFT element or the like.
Titanium nitride has light absorption efficiency much higher than aluminum or the like. For this reason, as regards the multilayered conductive layer (including the light-shielding layer) of titanium nitride and aluminum, there are problems in that much light is absorbed and heat is caused in the substrate.